Hi Cleo59,

just tried it with my Audya, and it works fine. I do not often use it, so it was not possible for me to answer faster.
I have the SW 5.0A

What I did to activate it:

Manual Bass must be activated (so that you can play it independent from the arranger)

In the Settings:

Menu/Keyboard Control/Accordeon

The Accordeon mode must be activated "Active"

With this I can change the sustain, octave etc.
The Bass sound itself depends on the current style selected.

Hope this helps

Joe